The present invention relates to a burner apparatus for the combustion of fuel and an oxidizer and especially to a burner apparatus in which the burner flame pattern can be controlled as to the shape and position within the combustion chamber.
The present burner is intended for use where adjustments to a particular flame pattern geometry is critical to the performance of the combustion process and is especially useful in applications where a variety of hydrocarbon fuels are constantly used and removal of the burner apparatus is not possible. The oxidizing medium is supplied to the combustion process by a series of ports that can be varied in momentum and resultant flow direction by simple adjustment of control valves. This adjustment provides the means necessary to utilize a variety of fuels, such as solid, liquid or gaseous, without the need to alter or remove the burner because of a fixed oxidizer design. The oxidizer ports can also be adjusted independent of each other allowing the flame geometry and direction to be changed as required. Variations in the oxidizer flow path enables optimization of thermal efficiencies while at the same time providing the means to minimize oxygen related emissions, such as those involving nitrogen and sulfur.
Current requirements of most industrial burners are not only to provide the necessary heat to the particular process but also to reduce unwanted combustion related pollution. More recently, oxygen/fuel burners (burners utilizing oxygen enriched air or pure oxygen) have been used to meet the emission reduction mandates. While meeting the required reductions, many of the oxygen/fuel burners do not provide the flexibility required by industry. Fixed geometrical configurations and the inability to use a variety of fuels and material limitations are some of the operational drawbacks associated with current oxygen/fuel burners.
The disclosed apparatus is specifically designed for flexibility of operation. Its oxidizer adjustability enables alterations to the flame pattern as required, such as load demand changes or heat transfer inputs. Heat transfer and flame shape vary with different fuels and adjustment capability is critical when a change to fuel type is made. The oxidizer variable momentum and resultant flow direction provide the diversity needed to acquire desirable flame results.
In order to meet the various operational requirements, the present invention is a burner where the oxidizer may have a variable momentum to obtain the needed limits of adjustments. The need for a high degree of adjustment is required to maintain safe and tolerable operation using a highly enriched oxidizer and to provide the means to utilize different fuel types while maintaining a consistently acceptable flame geometry and to enable performance adjustments for maximum attainable emission reductions.
Recently, burners utilize oxygen enriched air for efficiency improvements and emission reductions. With enriched air, there are additional problems with the burner operation. As oxidizer quality approaches near pure to pure oxygen, combustion temperatures increase and a higher rate of material degradation occurs. To counteract the elevated combustion temperatures, the burner uses a stabilized combustion away from the burner exit which enables heat transfer closer to the target and further from the burner, thereby increasing efficiency and extending burner/furnace equipment life. The ability to adjust the flame pattern away from the fuel and oxidizer ports for temperature sensitive equipment is even more critical as preheated oxidizers are used. Preheated oxidizers result in even higher combustion temperatures causing very rapid material degradation should flame patterns not be regulated. The adjustability aspect is important as it pertains to use with preheated oxidizer. Should oxidizer temperatures vary during a given interval, momentum changes can be performed to maintain consistent flame performance.
While the fuel (solid, liquid or gaseous) introduced has a particular momentum, it is in magnitude typically less than that of the oxidizer. This is not to say that the fuel momentum does not play a role in the flame pattern but rather to emphasize the degree of control it influences the overall reaction. Realizing this, control of the oxidizer is crucial in adjustment of the flame pattern in many operational situations, a change of hydrocarbon fuels is required. This change of fuel is readily incorporated by the burner's ability to vary oxidizer momentum. Solid fuels such as coal and wood possess much different transport and combustion characteristics than liquid fuels such as oil or alcohol. In turn, gaseous fuels such as natural gas and propane are different in the same regard as solid and liquid fuels. However, all these fuels are similar in their ability to be manipulated by an external oxidizer medium. A solid fuel is typically crushed into small particles and transported by a portion of the oxidizer, usually air, into the final combustion process. A liquid fuel is transported as a liquid and atomized into small droplets, usually in the form of an atomizing medium comprised of a portion of the oxidizer and introduced into the combustion process. Gaseous fuels are on occasion mixed with a portion of the oxidizer and introduced into the combustion process, but in most cases are transported and introduced as their original composition. The common factor in all three fuel types is that the fuel is supplied in particles, droplets or molecules small enough that it begins to display characteristics of a gaseous medium. This "mimicking" of a gaseous fuel allows the oxidizer momentum to have a considerable effect on the performance of the flame pattern. With the proper oxidizer momentum adjustment, acceptable flame patterns are achievable on the same burner while using different fuels. While the effect of fuel quality and fuel type cannot be ignored, the present invention does provide for the means to adjust oxidizer momentum to compensate for fuel variations.
The burner's adjustment capability also enable the operator to fine tune the performance to minimize any pollutants produced. A change in fuel will necessitate a change to the oxidizer flow configuration. This change will also effect the production of many pollutants in particular derivatives of nitrogen and sulfur. These derivatives are influenced by many factors, temperature and resident time among the most important. With the ability to adjust oxidizer momentum and in effect the flame pattern and temperature undesirable pollutants can be minimized, by adjustment, for any fuel used.
Momentum adjustment to the oxidizer is performed by varying flow among several ports. Four sets of ports are positioned about the fuel port to form a diamond shape fashion. The oxidizer ports are further divided into primary and secondary ports. The primary ports are closest to the fuel port and may have an angular direction toward the fuel. The secondary oxidizer ports are further away from the fuel and may be angled but not necessarily in the same degree as the primary ports. Depending on the required flame pattern, the oxidizer is diverted between primary and secondary ports. This diversion changes the overall momentum as well as the direction of the diverted flow, since primary and secondary ports may not pass the same angles or intersection points. In addition to diversion of oxidizer from primary to secondary, flow may be redirected away from or towards a particular port set. This provides the means necessary to redirect or compensate flame patterns for fuel changes, operational requirements or pollutants reduction.
In our prior U.S. Pat. No. 5,302,112 for a Burner Apparatus and Method of Operation Thereof, a combustion apparatus has independent flow streams, one for an oxidizer and one for a fuel with an adjustable control capability to permit various flame configurations and reproducible combustion rates at different oxidizer and gaseous fuel flow rates. A burner block was used having primary and secondary oxidizer passageways positioned at angles. The burner also had a gaseous fuel supply separated into primary and secondary gaseous fuel paths.
Other prior art U.S. patents may be seen in the Guillaume et al. U.S. Pat. No. 4,494,923, for an oxy-fuel burner having plural feed ports around an electric ignition system. The Anderson U.S. Pat. No. 4,378,205, is an oxygen fuel furnace having a plurality of oxidant jets positioned in a spaced relationship to a fuel jet and having a velocity sufficient to cause an aspiration of the furnace gases into the oxidant jets to mix the fuel. The Gitman U.S. Pat. No. 4,622,007, is for a variable heat generating method and apparatus which uses a hydrocarbon fuel having separately supplied streams of fuel and at least two oxidizing gases to react with the fuel. The Anderson U.S. Pat. No. 4,541,796, is an oxygen aspirator burner for firing a furnace having a plurality of oxidant jets in spaced relationship to the fuel jets. The Fioravanti et al. U.S. Pat. No. 4,954,076, is a nozzle mixed oxy-fuel burner using an oxidant fed at high velocity to aspirate recycled products of combustion. The Leikert, et al. U.S. Pat. No. 4,790,743, is a method of reducing NOX-emissions during combustion of fuel containing nitrogen which feeds a coal dust along with its carrier gas to a primary burner. The Fischer et al. U.S. Pat. No. 4,933,163, is a process of removing hydrogen sulfide from exhaust gas in which oxygen and air are fed through multiple tubes to the combustion chamber. The Ho U.S. Pat. No. 4,957,050, is a combustion process using oxygen or oxygen enriched air as an oxidant in which a liquid fuel is fed to the combustion chamber separate from the oxidants. The Delano U.S. Pat. No. 4,988,285, shows a combustion method in which oxidants are separately injected into the combustion zone in a defined velocity relationship and combustion gases are aspirated into the oxygen stream prior to mixture with the fuel. The Kobayashi et al. U.S. Pat. No. 5,267,850, is a fuel jet burner using a high velocity central fuel stream and a low velocity annular coaxial oxidant stream to carry out stable steady combustion in the expanding combusting stream. The Suzuki et al. U.S. Pat. No. 4,439,132, is for a method and apparatus for combustion with a minimal of NOX-emission and uses two valved air ports spaced from a fuel port.
The present invention has a central fuel feed which can be a gas, liquid, or solid fuel fed through the central fuel port into the combustion chamber and has the oxidants being fed into a plurality of spaced and positioned oxidant feed ports so that varying primary and secondary oxidant feeds for different sets of oxidant ports allows the alteration of flame patterns as required for different processes and allows heat transfer and flame shaped to vary for different fuels or other requirements. The oxidizers variable momentum and resultant flow direction provides the diversity needed for any desired flame result in an oxygen fuel burner.